Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$135.90	8.399%	$147.3142	$147.31	$147.30	$147.30
Purchase #2	$240.42	9.261%	$262.6853	$262.69	$262.70	$262.70
Purchase #3	$80.96	10.194%	$89.2131	$89.21	$89.20	$89.20
Purchase #4	$68.67	13.368%	$77.8498	$77.85	$77.85	$77.80
Purchase #5	$151.45	8.665%	$164.5731	$164.57	$164.55	$164.60
Purchase #6	$237.66	7.399%	$255.2445	$255.24	$255.25	$255.20
Purchase #7	$131.66	6.202%	$139.8256	$139.83	$139.85	$139.80
7 purchase totals =	$1,046.72		$1,136.7056	$1,136.70	$1,136.70	$1,136.60